1. Field of the Invention
The present invention relates to a power supply circuit that changes output voltages according to control signals.
2. Description of the Related Art
As conventional power supply circuits, various kinds of power supply circuits including a dropper type converter, a buck converter, and a switched capacitor converter have been known.
On the other hand, plural power supply voltages are required for low electricity consumption of an objective circuit, and it is not preferable to arrange low voltage wires in an integrated circuit from viewpoint of electricity consumption. Therefore, there is a demand for a power supply circuit that can change output voltages among plural values at a high speed.
When using the various kinds of power supply circuits described above for this purpose, it is necessary, in an changing output voltage from a high voltage to a low voltage, to discharge energy accumulated in load carrying capacity in the case of the dropper type converter system, and energy accumulated in load carrying capacity and energy accumulated in an inductor and a capacitor in a power supply circuit in the case of the buck converter system and the switched capacitor system.
On the other hand, in changing an output voltage from a low voltage to a high voltage, it is necessary to supply corresponding energy to load carrying capacity in the case of the dropper type converter system, and load carrying capacity and an inductor and a capacitor in a power supply circuit in the case of the buck converter system and the switched capacitor system. Therefore, enormous transition time is required in changing the output voltage from a high voltage to a low voltage, or vice versa, and any of the kinds of conventional power supply circuits is not suited for such a purpose.
One example of a power supply circuit of the buck converter system is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 2002-369505.